Fix: Uint and ULong.fromDouble() operations did not round

Author: Whathecode

kotlinx.interval.testcases/src/commonMain/kotlin/TypeOperationsTest.kt

@@ -85,6 +85,24 @@ abstract class TypeOperationsTest<T : Comparable<T>>(
         }
     }
 
+    @Test
+    fun fromDouble_rounds_to_nearest_value()
+    {
+        // Rounding only needed for evenly-spaced types.
+        val spacing = typeOperations.spacing
+        if ( spacing == null ) return
+
+        val next = typeOperations.unsafeAdd( a, spacing )
+        val aDouble = typeOperations.toDouble( a )
+        val nextDouble = typeOperations.toDouble( next )
+        val oneThird = (nextDouble - aDouble) / 3
+        val closerToA = aDouble + oneThird
+        val closerToNext = nextDouble - oneThird
+
+        assertEquals( a, typeOperations.fromDouble( closerToA ) )
+        assertEquals( next, typeOperations.fromDouble( closerToNext ) )
+    }
+
     @Test
     fun fromDouble_overflows_past_max()
     {

kotlinx.interval/src/commonMain/kotlin/BasicTypeOperations.kt

@@ -160,7 +160,11 @@ internal object UIntOperations : TypeOperations<UInt>
     override fun unsafeAdd( a: UInt, b: UInt ): UInt = a + b
     override fun unsafeSubtract( a: UInt, b: UInt ): UInt = a - b
 
-    override fun fromDouble( double: Double ): UInt = double.toUInt()
+    override fun fromDouble( double: Double ): UInt
+    {
+        val uInt = double.toUInt()
+        return if ( double - uInt.toDouble() >= 0.5 ) uInt + 1.toUInt() else uInt
+    }
     override fun toDouble( value: UInt ): Double = value.toDouble()
 }
 
@@ -174,7 +178,11 @@ internal object ULongOperations : TypeOperations<ULong>
     override fun unsafeAdd( a: ULong, b: ULong ): ULong = a + b
     override fun unsafeSubtract( a: ULong, b: ULong ): ULong = a - b
 
-    override fun fromDouble( double: Double ): ULong = double.toULong()
+    override fun fromDouble( double: Double ): ULong
+    {
+        val uLong = double.toULong()
+        return if ( double - uLong.toDouble() >= 0.5 ) uLong + 1.toULong() else uLong
+    }
     override fun toDouble( value: ULong ): Double = value.toDouble()
 }